I am building a triac based dimming circuit.

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Everything is working fine.

The problem which I am facing is when I turn on or off any appliance (NOT CONNECTED TO TRIAC) in my any other room, the CFL connected to my triac flashes in its off state., also flashes if I try to generate sparks in mains line.

Earlier I was using MOC3021 which was producing far more false triggers, and cannot use opto snubber as it leaks some current and connect appliance flashes every second.


You need a snubber—a resistor and capacitor, at least, to filter out transients and noise. A MOV wouldn't hurt, either. See page 7 of the Fairchild data sheet for the MOC3021, where they show this circuit:

Example snubber

You need to add the RS and CS shown on the right there. (If things are extremely noisy, they also have another example circuit in Figure 13 that filters things even more.)

  • \$\begingroup\$ Actually the triac I am using is snubberless, and I have also connected MOV across triac, but still I tried snubber circuit and the appliance connected stays on always. \$\endgroup\$ – Harmeet Singh May 2 '16 at 6:15
  • \$\begingroup\$ You're thinking of the definition backwards. A "snubberless triac" means the triac doesn't incorporate an internal snubber of its own, and that you will need to add one yourself in a noisy environment. Try the MOC3021 again and use the exact snubber component values from the datasheet, and leave out the MOV for the moment (that's for the long term protection of your triac). \$\endgroup\$ – JohnSpeeks May 2 '16 at 6:21
  • \$\begingroup\$ As I have already mentioned adding snubber to MOC3021 starts making CFL flash every second, so I switched to MOC3052 \$\endgroup\$ – Harmeet Singh May 2 '16 at 6:41
  • \$\begingroup\$ Try new components; you may have damaged yours. A snubber made of a functional resistor and capacitor with a functional MOC3021 will not cause oscillations. And try the alternate snubber circuit from Figure 13. \$\endgroup\$ – JohnSpeeks May 2 '16 at 6:58
  • \$\begingroup\$ Added a 100Ohm resistor between triac gate and T1 of triac and it solved the problem(electro-tech-online.com/threads/…), thank you for replying. :) \$\endgroup\$ – Harmeet Singh May 2 '16 at 7:59

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